This invention relates to a sealing apparatus for sealing semiconductor elements in a resin, and more particularly to an improved sealing apparatus which is compact and easy to maintenance.
FIG. 1 illustrates a conventional sealing apparatus for sealing a semiconductor element in a resin which was disclosed in Japanese Laid-Open Utility Model Application No. 59-9538. As shown in the drawing. the conventional sealing apparatus has a stationary lower platen 1 which rigidly supports four vertical guide rods 2. An upper platen 3 which is parallel to and confronts the lower platen 1 is secured to the upper ends of the guide rods 2. The guide rods 2 slidably support a movable platen 5 which can be moved up and down the guide rods 2 by an unillustrated reciprocating link mechanism which is driven by a servomotor 4 which is secured to the lower platen 1. The movable platen 5 rigidly supports a lower mold 6, and the upper platen 3 rigidly supports an upper mold 7 which confronts the lower mold 6. By moving the movable platen 5 vertically, the lower mold 6 can be brought into contact with the upper mold 7. The lower mold 6 and upper mold 7 have unillustrated cavities formed in the confronting surfaces thereof in which a semiconductor element is disposed during molding. The upper platen 3 and the upper mold 7 have axially-aligned through holes 3a and 7a, respectively, which are formed therein through which a resin for sealing a semiconductor element can be inserted into the molds 6 and 7.
Four parallel supports 8 (two of which are shown in the figure) extend vertically from the upper surface of the upper platen 3, and a flat mounting plate 9 is rigidly supported by the upper ends thereof. The mounting plate 9 rigidly supports a servomotor 10 and rotatably supports a first gear 11 and a second gear 12 which mesh with one another. The first gear 11 is directly driven by servomotor 10, and the second gear 12 is driven by the first gear 11. The second gear 12 is secured to one end of a threaded shaft 13 which is rotatably supported by the mounting plate 9 and the upper platen 3. One side of a movable plate 14 is slidably supported by two of the supports 8, while the other side of the movable plate 14 has a threaded portion 14a formed therein which engages with the threaded shaft 13, so that when the threaded shaft 13 is rotated by the servomotor 10 through the gears 11 and 12, the movable plate 14 is caused to translate in the vertical direction. A plunger 15 for inserting a resin tablet 16 into the molds 6 and 7 is secured to the movable plate 14 and extends through the holes 3a and 7a formed in the upper platen 3 and the upper mold 7, respectively.
Sealing of a semiconductor element using this conventional apparatus is performed as follows. A semiconductor element to be sealed is disposed in the unillustrated mold cavity of the lower mold 6, and the movable platen 5 is then raised by servomotor 4 until the lower mold 6 contacts the upper mold 7. A resin tablet 16 is placed in the through hole 7a in the upper mold 7, and servomotor 10 is driven to rotate the threaded shaft 13 through the gears 11 and 12, causing the movable plate 14 to descend and press the plunger 15 into the upper mold 7. The plunger 15 injects the tablet 16 into the cavities in the upper mold 7 and the lower mold 6 in which the semiconductor element is disposed. The resin tablet 16 is normally a thermosetting resin and is heated and made to set by a plurality of unillustrated cartridge-type heaters which are embedded in the upper and lower molds, thereby sealing the semiconductor element within the resin.
This conventional apparatus has the drawback that since the plunger 15 is directly driven by the threaded shaft 13, the threaded shaft 13 must be maintained parallel to the plunger 15, and there are restrictions on the locations in which the mechanism for rotating the threaded shaft 13 can be disposed. As a result, it is difficult to achieve decreases in the size of the apparatus. Furthermore, in order to replace or repair the plunger 15, it is necessary to remove the mounting plate 9, the gears 11 and 12, and the movable plate 14 from the vertical supports 8 before extracting the plunger 15 from the upper mold 7. Accordingly, the maintenance and repair of the apparatus are time-consuming.
Also, if it desired to arrange a plurality plungers in parallel so as to simultaneously seal a plurality of semiconductor elements in corresponding molds, it is necessary to form a plurality of through holes 3a in the upper platen 3 for the plungers to pass through. As the through holes 3a weaken the upper platen 3, and as the upper platen 3 must be able to support the weight of a separate drive mechanism for each plunger, it is necessary to increase the thickness of the upper platen 3 in order to guarantee adequate strength, resulting in a considerable increase in the weight of the apparatus.